Various abbreviations that appear in the specification and/or in the drawing figures arc defined as below:                ACK Acknowledgement        BS Base Station        CQI Channel Quality Indicator        CRC Cyclic Redundancy Check        CSI Channel State Information        CSR Channel State Report        CM Cubic Metric        DTX Discontinuous Transmission        DL Downlink        eNB evolved Node B        HARQ Hybrid Automatic Repeat Request        IDFT Inverse Discrete Fourier Transform        IRC Interference Rejection Combining        ML Maximum Likelihood        MMSE Minimum Mean Square Error        MRC Maximal Ratio Combining        MSC Modulation and Coding Scheme        NAS Non Access Stratum        PDCCH Physical Dedicated Control Channel        PDSCH Physical Downlink Shared Channel        PMI Precoding Matrix Indicator        PN Pseudo Noise        PUCCH Physical Uplink Control Channel        PUSCH Physical Uplink Shared Channel        QAM Quadrature Amplitude Modulation        QPSK Quadrature Phase Shift Keying        RB Resource Block        RE Resource Element        RI Rank Indication        RRC Radio Resource Control        SCH Synchronization Channel        SINR Signal to Interference plus Noise Ratio        SR Scheduling Request        TS Technical Specification        UCI Uplink Control Information        UE User Equipment        UL Uplink        
In a current LTE system, a UL control signal may be transmitted by two methods. In the first method, the UL control signal is transmitted on a PUCCH which can only be transmitted on those subframes that have not been scheduled to a PUSCH. The PUCCH supports a number of formats such that it can carry different types of control information, which may include but not limited to a HARQ-ACK, an SR, and a CSR including e.g., a CQI, an RI, and a PMI.
Unlike the first method, in the second method, the UL control signal at issue is transmitted on one subframe which has been scheduled for transmission of the PUSCH. In this case, the UL control signal will be multiplexed with a UL-SCH before DFT operations to reduce a CM for keeping properties of a single carrier. The second method is also referred to as UCI on PUSCH. The UCI, such as the CQI/PMI, HARQ-ACK, and RI, would be multiplexed with the PUSCH on a subframe.
When the PUSCH is employed to transmit the UL control information, the CSRs may be on an aperiodic basis, where an eNB requests CSRs from a UE by setting a CSI request bit in a scheduling grant. Since the CSRs have been explicitly requested by the eNB, their existence is known and appropriate rate de-matching can be done at the receiver. If one of configured transmission instances for a periodic report coincides with the UE being scheduled on the PUSCH, the periodic report is “rerouted” and transmitted on the PUSCH. Also, in this case, there is no risk of mismatch in rate matching; the transmission instants for periodic reports are configured by robust RRC signaling and thus the eNB knows exactly in which subframes such reports will be transmitted.
In contrast to the CSRs, a robust QPSK modulation is generally applied to one or two HARQ-ACK bits and these HARQ-ACK bits generally occupy the outermost constellation points for the PUSCH data symbols, regardless of the modulation scheme used for the data.
By virtue of a previous scheduling assignment on the PDCCH, the eNB knows when to expect a HARQ-ACK from the UE and can therefore perform appropriate demultiplexing of the HARQ-ACK part and data part. However, there is a certain probability that the UE may miss the scheduling assignment on the PDCCH, in which case the eNB will expect a HARQ-ACK from the UE while the UE cannot transmit one due to the previous missed scheduling assignment. If the rate-matching pattern were to depend on whether a HARQ-ACK has been transmitted or not, all the coded bits transmitted in the data part could be affected by a missed scheduling assignment, in which case it is likely to cause UL-SCH decoding to fail. To avoid such a failure, a possible approach is to puncture the HARQ-ACKs into a coded UL-SCH bit stream and thereby non-punctured bits would not be affected by the presence/absence of the HARQ-ACKs. Further, the potential problem of a mismatch between the rate matching in the UE and the eNB may be avoided.
To eliminate the impact due to a possibly missed scheduling assignment on the PDCCH, the 3GPP technique requires that the HARQ-ACK false detection probability as well as the HARQ-ACK missed detection probability, when multiplexed on the PUSCH, shall not exceed 1% at PUSCH power settings presented in table 8.2.5.3.1 in TS 36.141. This requirement poses a task to perform a DTX detection on HARQ-ACKs to ascertain or detect the presence/absence of HARQ-ACKs multiplexed on the PUSCH, which is not a trivial challenge.
For the UCI on PUSCH as discussed before, a possible DTX detection approach may involve applying an existing demodulation solution to perform soft demodulations and get soft bits for all REs of the used RBs on one subframe, sorting out the soft bits for each type of information, including the PUSCH data, HARQ-ACK, CQI/PMI, RI or the like, and feeding those sorted out bits into a corresponding detection module for a DTX detection.
In the above DTX detection approach, all the HARQ-ACK soft bits would be used to obtain a metric and then compare the metric with a threshold to detect whether the HARQ-ACK has been transmitted or not. The selection of a proper threshold may heavily rely upon extensive PUSCH link level simulations, which are rather static and not adaptive enough towards any combinations of the allocated bandwidth, MCS, SINR and beta offset. It is shown by the PUSCH link level simulations that the soft bits based solution cannot meet the requirements of the HARQ-ACK error detection probability performance or the HARQ-ACK false alarm probability performance, which has been specified in 3GPP TS 36.141, v9.6.0, section 8.2.3.